Abstract:Horizontal sublevel top coal caving mining technology(HSTCC)is currently one of the effective mining methods for steeply inclined extra-thick coal seams.With the continuous improvement of equipment and technical levels,the sublevel height and production capacity of the panel are constantly increasing,and the level of intelligence is also continuously improving.This paper systematically summarized the historical process of HSTCC,and took the Wudong Coal Mine of Xinjiang Energy as an example to introduce the latest progress of HSTCC with the near-vertical seam,which belongs the relatively large dip angle in steeply inclined seams.The stress distribution characteristics and evolution laws of HSTCC were investigated,and the fracture models of the roof and floor of the panel and the rock pillars of the coal seam group were established.The reasonable roadway layout position was discussed,ensuring the dual goals of maximizing the top coal recovery ratio and economic rationalization.The theoretical e-quations of the drawing body and the top coal boundary under the influence of the inclination boundary of the roof and floor were derived.The end-full and multi-round sublevel reverse se-quence caving methods have been developed,which greatly reduced the coal loss of the whole HSTCC panel.High recognition accuracy and self-cleaning dust-proof cameras have been de-veloped,and an image recognition intelligent caving system and electro-hydraulic control signal communication architecture have been established,achieving intelligent caving control in HSTCC panels.The research results have scientific guiding significance for improving the top coal recovery and the stability of surrounding rock in HSTCC panels.

Abstract:Compared with shallow engineering,deep underground engineering is characterized by complex,coupled geological conditions,including high in-situ stress,high geothermal tem-perature,and high seepage pressure.Under the influence of engineering geological activities,these conditions exhibit long-term dynamic evolution,resulting in frequent hazards with high energy release that are difficult to control.Such challenges persist throughout the entire pro-ject lifecycle,spanning investigation,construction,operation and maintenance,and remedia-tion,and therefore call for a comprehensive inspection system covering the full lifecycle of deep underground engineering.In this context,Unmanned Aerial Vehicles(UAVs),leveraging three-dimensional mobility and integrated capabilities in environmental perception,localization and mapping,and flight control,can provide an intelligent solution for integrated management of safety,quality,and cost.Accordingly,this paper systematically reviews the research pro-gress in intelligent UAV inspection technologies for deep underground engineering,and the main findings are summarized as follows.Intelligent UAV inspection is systematically applied to perform five categories of tasks,namely modeling and geological analysis,structural health monitoring,environmental monitoring,production progress monitoring,and emergency re-sponse.An imaging,three-dimensional,and temporal data processing framework is also sum-marized.Through within-domain processing and cross-domain fusion,raw data are trans-formed into state indicators and risk levels that support engineering decision making.A sensor configuration logic driven by environmental factors is established,and a complete preprocess-ing chain covering spatiotemporal alignment,data cleaning,and quality assessment is summa-rized.This provides a solid foundation for maintaining stable perception of intelligent UAV in-spection systems in degraded environments.The reliability of UAV localization and mapping is emphasized to depend on a full-chain technical system capable of degradation self-diagnosis and global consistency maintenance.Robustness should be embedded in registration,odometry,loop closure detection,and back-end optimization,and geometric and semantic information should be integrated to suppress drift and mismatches.Multiple technical pathways are sys-tematically reviewed,ranging from macroscopic path search to microscopic real-time obstacle avoidance.It is indicated that a successful planning system should deeply integrate environ-mental uncertainty,dynamic constraints,and task semantics.Based on insights into current technical barriers,this paper further proposes specific development directions centered on plat-form sensing,localization and mapping,planning and obstacle avoidance,intelligent algo-rithms,computing collaboration,and communication and energy,aiming to achieve break-throughs through synergistic advances across multiple technological chains and to promote the application and expansion of fully autonomous intelligent inspection paradigms for deep under-ground engineering.

Abstract:As coal mining progresses deeper,the characteristics of high stress and high temper-ature become more pronounced in deep mining.A true triaxial deep rock mechanics test system has been developed to investigate the rock mechanics characteristics and roadway failure mech-anisms under high stress and high temperature.The specimen size used in this device is 100 mm× 100 mm× 100 mm.It can provide a maximum force of 2100 kN and a temperature of 150℃.The apparatus can simulate complex environments characterized by high stress and high temperatures.The following research and development have been carried out to address the de-fects of difficult synchronization and easy eccentricity during loading of the true triaxial testing device,as well as uneven heating of the sample:A dual actuator with the same origin has been designed,which automatically aligns and achieves synchronous mechanical loading of any size combination load in three directions;Heating rock samples by generating thermal radiation through heating a closed pressure chamber.Two special designs solve two technical problems in the field of real-time high-temperature true three-axis loading.Based on this system,pre-liminary tests were conducted on the mechanical properties of rock loading and unloading,as well as simulation tests on tunnel failure at different stress angles.The good experimental ac-curacy and rich scalability of the system have been verified.The research and development de-vice provides a reliable experimental basis for rock mechanics research and geological hazard prevention under complex deep conditions.

Abstract:To achieve accurate identification of rock mass discontinuities,a density-adaptive im-proved region growing algorithm was proposed to address the poor performance of conventional region growing methods on 3D point clouds with highly non-uniform density and fixed global thresholds.Based on the local point-cloud density,adaptive threshold functions were construc-ted,and a post-processing strategy combining small-cluster filtering and an unclassified-point voting scheme under smoothness and coplanarity constraints was designed to enhance the geo-metric continuity of the extracted discontinuities.In addition,hyperbolic tangent functions were employed to achieve smooth transition adjustment of the curvature threshold and the nor-mal-angle threshold.Sedimentary rock and orthoquartzite slope outcrop point-cloud datasets were used for comparative experiments and engineering verification.The results show that the average dip error and dip-direction error of the identified discontinuities sets range from 0.24° to 2.60°and from 0.43°to 2.90°,respectively,which satisfies engineering accuracy require-ments.This study provides an effective approach for parameter self-adaptive adjustment in dis-continuities identification from 3D point clouds.

Abstract:Accurate determination of in-situ coal seam gas pressure and its desorption behavior is essential for effective gas extraction and outburst prevention.The"deep coal seam in-situ pressure-preserving gas coring method"calculates the in-situ gas pressure based on the gas pressure before and after the coal core undergoes re-equilibration within the pressure-preser-ving chamber.The accuracy of this calculation critically depends on precisely characterizing the volume expansion-pressure re-equilibration process within the coring device.This study inves-tigates the inhibitory effect of moisture on gas desorption through atmospheric pressure de-sorption tests.Continuous expansion desorption tests were conducted to directly simulate the stepwise volume increase process within the corer,revealing the impact of moisture content on pressure evolution.Low-field nuclear magnetic resonance(NMR)analysis elucidated the dual inhibition mechanism of moisture on gas desorption-diffusion:competitive adsorption and pore blockage.Building on these findings,an in-situ gas pressure measurement method was devel-oped and field-validated in a mine in Jincheng,Shanxi Province.The results show that:Mois-ture significantly inhibits gas desorption;under comparable pressure conditions(approximate-ly 2.5 MPa),increasing the moisture content to 5.11％the total desorption volume in 150 min(Q150)is reduced by 72.3％and the desorption volume in the first minute(Q1)by 84.5％compared to dry samples.During continuous expansion desorption(initial pressure:3.33 MPa,five stepwise expansions),the equilibrium pressure decreases linearly with increasing moisture content;the final equilibrium pressure for the sample with 4.85％moisture content is 6.25％lower than the dry sample.Pressure rebound amplitude also attenuates significantly with successive expansions.Field application of the method,which inversely calculates the in-situ pressure using measured pressure data from the pressure-preserving corer and sample pa-rameters,demonstrates high reliability for water-bearing coal seams(moisture content:5.08％-6.68％),with the overall error below 5％compared to the measured in-situ pressure(0.69 MPa).

Abstract:In-situ leaching mining of sandstone-type uranium ores is based on the technical prin-ciple of water retention and pressure stabilization,whereas longwall mining of coal mines takes dewatering and pressure reduction as a safety prerequisite.The contradiction in their co-mining is essentially a conflict regarding the spatial demand for the groundwater system.To funda-mentally alleviate the contradictions in the co-mining of coal and uranium resources,a method for determining the reasonable offset distance for the coordinated development of coal and ura-nium is proposed based on the interaction mechanism of coal-uranium co-mining.The disturb-ance characteristics of the uranium-bearing aquifer caused by the four stages,namely coal mine roadway exposure,pre-mining dewatering and drainage,mining operation,and post-mining closure,were systematically analyzed.On this basis,the optimal orientation of the offset dis-tance perpendicular to the regional groundwater flow direction was determined,and based on the requirement of in-situ leaching uranium mining for confined water head,the principle for determining the reasonable offset distance to prevent the groundwater drawdown funnel caused by coal mining from crossing the boundary to the uranium mining area was established.Based on the big well theory,a calculation model for the influence radius of the groundwater draw-down funnel caused by coal mining was established under two occurrence modes,namely"up-per coal and lower uranium"and"upper uranium and lower coal".According to the established model,the reasonable offset distance for coordinated mining of two typical coal-uranium sym-biosis modes in the southern margin of the Ili Basin and the northern part of the Ordos Basin was quantitatively determined.The results show that under the layout conditions perpendicu-lar to the regional groundwater flow direction,the minimum required safety offset between Ili No.1 Coal Mine and the Kujiertai-Honghaigou Uranium Mine is 2.7 km,while a minimum safety distance of 7.5 km is required between the Tarangaole Coal Mine and the Nalinggou U-ranium Mine.

Abstract:To investigate the influence of polymer coating support on the impact resistance of coal,this study aims to reveal its mechanical characteristics and energy dissipation behavior under coupled dynamic-static loading.Split-Hopkinson Pressure Bar(SHPB)system,coupled dynamic-static loading tests were conducted on coal samples prepared with three different poly-mer coating thicknesses:0 mm(uncoated),1 mm,and 2 mm.The samples were first subjec-ted to a constant hydraulic oil pressure of 0.25 MPa,followed by five low-energy cyclic im-pacts(driven by 0.2 MPa air pressure)and one high-energy impact(driven by 0.3 MPa air pressure).The experimental results indicate the following:Mechanical Characteristics:The polymer coating significantly enhanced the dynamic peak stress and peak strain of the coal sam-ples,thereby improving their dynamic strength and deformation capability.Compared to the uncoated samples,the peak strain and peak stress of the 2 mm coated sample under high-ener-gy impact increased by approximately 54.65％and 44.69％,respectively.Additionally,the coating layer reduced the dispersion of the stress-strain curves during cyclic impacts,indicating a more stable mechanical response.Energy Characteristics:The coating layer improved energy coupling properties by reducing the proportion of reflected energy while effectively increasing the proportion of dissipated energy.This also resulted in more stable energy dissipation under cyclic impacts.Under high-energy impact,the reduction in dissipated energy for the 2 mm coated sample was only 11.51％,significantly lower than the 24.31％observed in the uncoated sample,demonstrating superior impact resistance.Failure characteristics:The polymer coat-ing effectively suppressed the degree of fragmentation.As the coating thickness increased,the specimen integrity was significantly enhanced.The mass ratio of detached coal fragments de-creased from 0.54(0 mm coated sample)to 0.01(2 mm coated sample).In conclusion,the polymer coating effectively improves the overall load-bearing capacity and impact resistance of the coal body,significantly enhances its energy dissipation capability,and transforms the vio-lent impact failure into a more gradual energy release process.This holds positive implications for the prevention and control of coal bursts.

Abstract:Deep coal mines are associated with abundant karst geothermal resources.However,their naturally low permeability significantly constrains the efficient exploitation of these re-sources.This study proposes utilizing the pressure-relief zone formed in the floor strata after longwall mining to activate fracture apertures and achieve self-enhanced permeability in the reservoir,offering a promising new pathway for efficient geothermal development.For this purpose,a thermal-hydraulic-mechanical(THM)fully coupled model was established specific-ally for mining-induced reservoir activation for geothermal extraction.The model characterized the distribution of fracture aperture and permeability under mining influence,revealed the dy-namic evolution of geothermal production efficiency during the activation process,clarified the mechanism behind enhanced heat extraction in the activated reservoir,and proposed a method for synergistic and efficient co-development of deep coal and geothermal energy.The results indicate that mining-induced effects reduce the normal stress on fractures in the goaf floor,triggering shear dilation or tensile opening effects that significantly increase fracture apertures,leading to the formation of a funnel-shaped high-permeability zone in the floor reservoir.Min-ing activities enhance the average flow velocity within the channels,expand the effective flow range,and improve the heat transfer efficiency during cold fluid reinjection.As the mining dis-tance increases,both reservoir permeability and heat extraction efficiency improve rapidly ini-tially,followed by a gradual slowdown in the rate of enhancement.A"mining-first,heat pro-duction-follows"approach for coordinated coal-geothermal development is proposed,wherein high-permeability zones in the floor strata are delineated following mining face advancement,followed by the deployment of wells along its major axis to achieve efficient geothermal re-source extraction.This study provides theoretical support for the integrated development of coal and geothermal energy and offers a novel approach for the enhancement of low-permeabili-ty geothermal reservoirs.

Abstract:Mineral resources serve as fundamental assets for national economic development and defense infrastructure.Screening,a critical within the mineral processing chain,faces signifi-cant challenges with difficult-to-screen ores characterized by high surface moisture,severe sli-ming,and a high proportion of near-size particles.These characteristics often lead to the fail-ure of conventional centralized excitation rigid screening,thereby severely constraining the ef-ficient utilization of mineral resources.Addressing the bottleneck in efficiently screening vis-cous fine-grained minerals,this study elucidates two pivotal scientific issues:The dispersion behavior of multi-component aggregates and the mechanism of screen aperture blinding,and the evolution mechanism of the temporal and spatial distribution of particles under interactive impact with the screen surface.This study commenced with a systematic review of theoretical and technological advancements in screen surface structure,excitation methods,and screen machine design.Based on this foundation,a rigid-flexible coupled self-cleaning screening method and a variable-amplitude excitation technique were developed.A dynamic design proce-dure integrating key structural and process parameters was established.Furthermore,the in-telligent identification and fault early warning system for screening status were developed.These collective innovations have successfully enabled the highly efficient and deep screening of viscous fine-grained minerals,providing a viable and effective pathway for enhancing the pro-cessing efficiency of difficult-to-screen ores.

Abstract:In-situ modification mining fundamentally redefines the traditional"excavation-and-transportation"mode of underground resource extraction.This innovative approach enhances reservoir permeability and reactivity by injecting physical or chemical fluids into target forma-tions,thereby triggering coupled thermal-hydraulic-mechanical-chemical(THMC)processes.These processes selectively convert valuable solid minerals into extractable fluid phases,offer-ing notable advantages including reduced environmental disturbance,high operational efficien-cy,and improved sustainability.This paper provides a systematic review of the theoretical and technological framework of in-situ modification mining,with particular emphasis on its central scientific challenge:Elucidating the dynamic response of evolving pore-fracture systems under multi-physical field coupling.We establish mathematical models for three representative types of evolving media-those with residual solid skeletons,those without skeletons,and those dom-inated by fracture evolution.These models capture the spatiotemporal evolution of pore-frac-ture networks and clarify their governing role in fluid transport throughout the modification process.At the theoretical level,establishing a multi-scale and multi field coupling model for the evolution of pore fracture media is the core of achieving in-situ modification green and effi-cient mining.At the same time,integrating uncertainty quantification and physical data-driven machine learning methods,and constructing efficient and reliable proxy models,can achieve accurate prediction and intelligent control of the in-situ modification and efficient mining process of deep resources.At the technical application level,three composite modification tech-nology paths have been proposed:Coal seam reservoir volume fracture network construction technology that combines mining pressure relief and key layer fracturing,coal seam interface fracturing and pyrolysis gasification technology,and CCCUS technology for deep coal seam su-percritical CO2 fracturing displacement and biotransformation of CH4.The technological evo-lution from single modification to composite modification is an inevitable choice to break through the bottleneck of efficient and green mining of deep and complex geological conditions in resource reservoirs,and has important guiding significance for promoting the transformation and upgrading of mineral resource development models.

Abstract:The accurate and dynamic prediction of surface movement and deformation by over-burden bed separation grouting filling is of great significance for the early warning and protec-tion of surface building deformation.Considering the direct influencing factors of surface movement and deformation caused by overburden bed separation grouting filling,a CNN conv-olutional neural network LightGBM prediction model based on GA genetic algorithm optimiza-tion(GA-CNN-LightGBM model,GCL model)for overburden separation grouting surface movement and deformation is constructed using multi-source data such as working face produc-tion data,overburden bed separation grouting filling data,and surface movement and deforma-tion data as data sources.At the same time,the reliability of the model is tested by the four indexes of the mean absolute error(EMAE),the root mean square error(ERMSE),the coefficient of determination(R2)and the residual error(ε).And the method has been successfully ap-plied to the prediction of surface movement and deformation at the 3801 working face in Huo-erxinhe coal industry.The results show that the GCL model was trained to predict surface tilt using multi-source data collected during the mining process in front of the 3801 working face of Huoerxinhe Coal Industry.After training,the maximum residual of the GCL model's surface tilt prediction was less than 0.1 mm/m,with EMAE and ERMSE of 0.029 mm/m and 0.037 mm/m,respectively.The deviation between the predicted value and the measured value was relatively small.R2 is 0.967,indicating a high degree of model fitting and meeting the require-ments of dynamic prediction.In the application of surface tilt prediction in the surface oil stor-age tank area of the 3801 working face of Huoerxinhe Coal Industry,the GCL model has a maximum residual of 0.075 mm/m for surface tilt prediction,which is less than 0.1 mm/m.The EMAE and ERMSE are 0.039 mm/m and 0.042 mm/m,respectively.The R2 is 0.941.The degree of deviation between the predicted values and the measured values,and the degree of model fit,both demonstrate that the model has good predictive performance.During and after the 3801 working face,the actual maximum tilt of the oil storage tank was less than the warn-ing value of the tank.The GCL model dynamically predicted and ensured the safe mining of the working face without shutting down the Sinopec gas station.The research results can pro-vide theoretical and technical support for related projects.

Abstract:Coal is a crucial energy and industrial raw material in China.During coal mining and coal-fired power generation processes,a large number of coal-based solid waste such as fly ash and coal gangue will be produced,which will seriously pollute the ecological environment for a long time.The absorption and sequestration of CO2 using substances containing alkaline com-ponents is regarded as one of the most promising carbon reduction technologies.Fly ash and gangue widely used in goaf grouting for fire prevention and extinguishing contain alkaline com-ponents such as CaO and MgO,thereby exhibiting the potential for CO2 mineral carbonation sequestration.Through the absorption and mineralization of CO2 by fly ash and coal gangue slurries,followed by the injection of mineralized products into goafs to prevent and control coal spontaneous combustion,a synergistic effect between mineral carbonation and disaster preven-tion/control can be achieved.An integrated technology for carbon sequestration via coal-based solid waste mineralization and goaf sealing for fire prevention and control is presented in this paper.The research progress of coal-based solid waste and CO2 mineralization technologies is systematically reviewed;the variation laws of the physicochemical properties and structures of coal-based solid waste after CO2 mineralization reaction are analyzed;and the inhibitory char-acteristics of mineralized products on the heating rate and heat release during coal spontaneous combustion are clarified.To further promote the development and large-scale application of the integrated technology of coal-based solid waste mineralizing CO2 and coal spontaneous combus-tion disaster prevention and control,three key challenges are identified:low reaction efficiency during the mineralization process of solid waste slurry,lack of integrated technology of CO2 mineralization-grouting for fire prevention,and insufficient understanding of the safety and en-vironmental implications of mineralized products stored in goafs.Correspondingly,the re-search directions and contents of mineralization reaction process enhancement,efficient fire prevention and extinguishing utilization of mineralized products,and long-term safe storage in goaf are proposed.There is an urgent need to study the occurrence forms and leaching patterns of calcium/magnesium elements in coal-based solid wastes,develop new technologies for effi-ciently leaching calcium and magnesium ions from slurry and rapidly dissolving CO2,innovate integrated technical equipment and intelligent control system for mineralization CO2-grouting fire prevention,elucidate the physicochemical inhibition mechanism of mineralized products on coal spontaneous combustion,and clarify the carbon sequestration stability of mineralized products as well as environmental friendliness in goaf.This integrated technology will promote the development of the entire chain of basic research-equipment research and development-engineering application,and further provide support for the low-carbon resource utilization of coal-based solid waste and the national"double carbon"goal.

Abstract:The typical complex multiphase flow disasters of coal dust explosions pose a persis-tent and significant threat to national energy stability and development.In-depth research on the chain reaction and energy transfer mechanism of coal dust explosions is crucial for maintai-ning the efficient operation of the energy supply chain and promoting the safe development of the coal industry.This study reviewed the current status of coal dust explosions and the char-acteristics of gaseous products,and clarified the early pyrolysis fracture sites of coal macro-molecules while quantifying bond energy distribution.From the perspective of chemical kinet-ics,the main reaction paths and key free radical evolution laws of volatile gas in coal dust ex-plosion were expounded.The energy transfer framework based on the axial partition and radial stratification of the explosion cavity was proposed,and the spatial non-uniformity mechanism of heat and mass transfer and energy accumulation in the multi-phase medium during the ex-plosion process was revealed.The macroscopic and microscopic full-chain system from molecu-lar bond fracture to system energy release was constructed,and the influence of chain reaction on the initiation,expansion and termination of the explosion was clarified.The results show that coal dust explosions originate from the instantaneous high-temperature pyrolysis of pul-verized coal particles,and its essence can be regarded as a composite reaction system driven by solid-phase pyrolysis and dominated by gas-phase explosion.Under the influence of an external heat source,the C—C bonds of the aliphatic side chains connecting aromatic clusters in the en-ergy-optimized coal macromolecular structure are the preferred initiation sites for pyrolysis breakage.The combustible gas film formed by the escape of volatile components and free radi-cals form a chain exothermic cycle by radiation heating adjacent unburned particles,which di-rectly drives the explosion reaction to diffuse rapidly from point to surface.The axial partition and radial stratification in the explosion cavity cause energy and matter to be concentrated and transported along preferential channels with low impedance or strong drive,resulting in the heat release and energy accumulation of chemical reaction highly concentrated in localized are-as,aggravating the instability of the system and intensifying the formation of destructive shock waves.This study provides theoretical support for the risk assessment of coal dust explosion and the formulation of prevention and control strategies.

Abstract:Hydraulic fracturing is one of the primary methods for stress relief in roadway sur-rounding rock(RSR).Great convergence difficulty,unclear interaction mechanism between fracture networks and stress evolution of RSR are encountered in the simulation of hydraulic fracturing in roadway roof.Based on phase field theory,the effective inversion of hydraulic fracturing crack propagation and surrounding rock stress relief in roadway roof was achieved by introducing initial energy terms into the potential energy equation and combining with initial stress balance technique.The fracturing range,fracturing degree and complexity of roadway roof crack networks were quantitatively characterized with damage area,damage density and fractal dimension as core indicators,and the mapping relationship between roof crack charac-teristics and surrounding rock stress relief effects was established.The results show that:The model exhibits high consistency with experimentalfracture propagation trajectories and demon-strates high accuracy for hydraulic fracturing calculations.The propagation behavior of subse-quent hydraulic fractures is controlled by pre-existing fractured cracks through regulating the roof stress field.Under the synergistic action of multiple fractures,high stress at crack tips is weakened and the transmission path to RSR is blocked,thus an effective stress relief zone is formed in RSR.The stress relief effect of RSR is negatively correlated with damage area,while positively correlated with damage density and fractal dimension.The stress relief effect of RSR follows a nonlinear evolution pattern of'first decreasing then increasing'as the lateral pressure coefficient increases from 0.8 to 1.6,with the optimal effect at a lateral pressure co-efficient of 0.8 and the worst effect at 1.2.To ensure better pressure relief effects in RSR,the fracturing spacing can be appropriately reduced and the inter-borehole angle increased to form high-density and high-complexity fracture networks.The research findings can provide certain engineering guidance for fracturing design.

Abstract:To explore the distribution characteristics of the fracture field and the law of pres-sure-relief gas storage and migration in the goaf under the condition of fully mechanized top coal caving mining in an inclined extremely thick coal seam,and to study the optimization mechanism of gas extraction methods,a large-scale two-dimensional physical similarity simu-lation experiment was carried out in a gassy coal mine.The movement form of overlying strata in the stope was analyzed,the stress evolution characteristics of the overlying strata were ob-tained,the displacement,angle,and probability entropy change characteristics of the overly-ing strata were calculated.The formation mechanism of"similar cooling tower"in pressure re-lief gas transportation and storage area was clarified,the development form of gas transporta-tion and storage area was deduced,the mathematical theory control model of gas transporta-tion and storage area was constructed,and the pressure relief gas drainage technology was pro-posed.The results show that under the condition of fully mechanized caving mining in an in-clined thick coal seam,the pressure-relief gas transportation and storage area exhibits a"cool-ing tower"distribution pattern.The maximum stress change value in front of the coalwall side of the transportation and storage area is 37 MPa,and the stress concentration coefficient is 7.60.The bulking coefficient of the overburden rock shows an asymmetric distribution charac-teristic of"high on both wings and low in the middle",and the bulking coefficient increases from 1.19 to 1.61.In addition,PCAS image analysis software was used to obtain the distribu-tion law and spatial relationship of voids and cracks.The development degree of the crack structure on the open-off cut side is significantly more complete than that on the working face side.A fractal dimension of 1.28 and a crack length of 15 mm are defined as the judgment pa-rameter indexes of the pressure-relief gas transportation and storage area.Considering the mi-gration,diffusion,and reservoir form of gas in the goaf,a mathematical theoretical control model of the pressure-relief gas storage area in the inclined thick coal seam was established,and a boundary calculation formula for the pressure-relief gas storage area was derived.This model guides the design of the layout parameters of high-level directional long boreholes and has achieved favorable extraction results.The research results have been preliminarily applied in the Liuhuanggou coal mine,which provides a theoretical reference for the efficient extraction of gas in fully mechanized caving mining in inclined extremely thick coal seam and ensures the safe and efficient mining of mines under similar conditions.

Abstract:To address the challenge of controlling large deformations in squeezing soft rock for-mations in the tunnel excavation using tunnel boring machine(TBM)and to enhance the a-daptability of TBM construction techniques to major engineering hazards,a high-strength sup-port technology utilizing square steel tube concrete arches was introduced.Flange connection joints for the arches with different structural configurations were designed,and the strength,stiffness,and ultimate deformation capacity of joints with different flange designs were com-paratively analyzed.Furthermore,mechanical loading tests were performed on composite structures comprising SSTC arches and shotcrete layers.These tests elucidated the ultimate strength and failure modes of the composite structure under varying arch spacing conditions.Eigenvalue buckling analyses of multi-unit arch assemblies under different spatial constraint conditions were carried out,clarifying the influence mechanism of spatial connection states on the critical buckling strength governing spatial instability.Field implementation trials of the SSTC arches were conducted,the effectiveness of the design scheme in controlling large soft rock deformations was validated.The results demonstrate that:The yield strength and ulti-mate strength of the continuous flange joints are 1.41 and 1.55 times higher,respectively,than those of non-continuous flange joints.Furthermore,the ultimate deformation capacity of the continuous joints is 3.35 times greater than that of the non-continuous joints.The peak load-bearing capacity of the composite support structure exhibites a decreasing trend with in-creasing arch spacing.The fifth-order buckling modes of the arches consistently manifestes as out-of-plane instability.The scope and density of longitudinal connections significantly influ-enced the spatial stability of the multi-unit arch assemblies.Field comparative monitoring re-veales that the maximum stress in conventional H200 steel arches reaches 400 MPa,whereas it is only 150 MPa in the SSTC arches.This indicates that the SSTC arches possess a superior strength reserve capacity and offer enhanced control over surrounding rock deformation.This research provides crucial theoretical and empirical support for the mitigation of large deforma-tion hazards in TBM-excavated tunnels through squeezing soft rock strata.

Abstract:To further investigate the mechanism by which in-seam geo-stress influences the disas-ter-causing effects of coal-gas outburst two-phase flow in roadways,physical simulation experi-ments of outbursts under different geo-stress conditions were conducted.The disaster-causing characteristics of the two-phase flow during outbursts were analyzed,including impact dynamics,movement,and pulverized coal accumulation-sorting.The results show that the frequency of im-pact force pulses shows a decreasing trend as the distance from the outburst mouth increases.The peak impact force in the near outburst mouth area is positively correlated with geo-stress.As dis-tance increases,the attenuation of the peak impact force accelerates,with a notably lower decay rate under high geo-stress conditions.The disaster-causing zone of impact dynamics within the roadway exhibits a discontinuous distribution,primarily concentrated in the middle-front sections.The highest risk period occurs between 600 and 2 000 ms after the outburst.The harmfulness of impact dynamic disaster-causing in the roadway shows a trend of first increasing and then decrea-sing with increasing geo-stress,and decreases significantly under high geo-stress.It indicates that when the geo-stress increases to a certain level,a suppression mechanism for disasters caused by two-phase flow impact dynamics will be generated.The speed of outburst shock waves ranges from 330 to 400 m/s,approximately 10 to 15 times faster than the pulverized coal flow.During the outburst process,the pulverized coal concentration in the area near the outburst mouth chan-ges at the fastest rate,and the higher the geo-stress,the greater the pulverized coal concentration.With the increasing geo-stress,both the total mass of pulverized coal after outburst and the pro-portion of small and medium-sized particles increase,which both enhance the outburst intensity and exacerbate pulverized coal fragmentation.The peak value of crushing work migrates backward along the roadway with the increase of geo-stress,and the amplitude tends to increase.The accu-mulation and crushing energy of pulverized coal is mainly concentrated in the middle of the road-way.

Abstract:To study the load-bearing damage characteristics of coal samples with drill holes in high gas environments,five kinds of load-bearing damage tests of coal samples with drill holes under gas pressure were carried out by using a real triaxial mechanical test system with one-side visualization and gas sealing function,and image information of the damage process of the samples under direct observation was obtained,and the characteristics of the borehole dynam-ics damage in the process of load-bearing and the evolution of the cracks on the surface of the samples were analyzed by combining with the DIC and acoustic emission monitoring technolo-gy.The results show that three types of typical dynamic damage phenomena,such as particle ejection,coal body throwing and debris spalling,will gradually appear in the process of drilling damage,and the whole damage process shows discontinuous and intense dynamic damage char-acteristics,with particle or debris ejection appearing in the drilling wall first,followed by in-tensive coal body throwing and debris spalling,and collapsing of the wall in the late stage of the damage.The existence of gas gas weakens the intensity of damage,and with the increase of gas pressure,the damage of the borehole gradually changes from intense particle ejection(coal body throwing)to debris spalling,and the average ejection velocity of particles(debris)gradually decreases in the range of test gas pressure(0～1.2 MPa),from 0.345 m/s to 0.197 m/s,with the decrease of about 42.9％.The emergence and expansion of cracks on the surface of coal samples coincide with the sudden change points of stress,strain and acoustic emission signals,and the damage process of coal samples can be divided into four stages:Accumulation of strain energy,damage of coal body above the drill hole,damage of coal body below the drill hole and crack penetration.In the test gas pressure range(0～1.2 MPa),the length of the strain energy accumulation phase decreased gradually with the increase of gas pressure,from 127 s to 84 s,with a decrease of about 33.6％,and the cumulative acoustic emission energy and counts were negatively correlated with the gas pressure,with a decrease of 92.2％and 98.5％,respectively.Cracks began to emerge around the borehole under the influence of shear,and gradually appeared to arch under the composite effect of tension shear,followed by crack penetration.Under the effect of shear,the cracks started to sprout around the drill hole,and gradually showed arch shape under the compound effect of tensile shear,and then the cracks gradually increased under the effect of tensile shear,and the coal body in the area of the drill hole showed the overall instability.The damage cracks on the surface of the coal samples showed the arch shape,and the largest area of the arch surrounded by cracks showed negative correlation with the gas pressure,which was reduced from 748.27 to 394.9 cm2,with a reduc-tion of about 47.2％.The strain localization phenomenon on the surface of the coal samples gradually intensified with loading.The phenomenon of strain localization on the surface of the coal samples gradually intensified with the loading,and the effective variance of the strain field accelerated,forming"X"shaped horizontal strain localization zone,"butterfly"shaped shear strain localization zone and"strip"shaped vertical strain localization zone on the surface of the coal samples.The area of the shear strain concentration zone corresponding to the region of the largest arch crack is negatively correlated with the gas pressure,which decreases from 47.89 to 27.90 cm2,with a decrease of about 41.7％.

Abstract:Grout-based sealing of fractures is an important method for alleviating air leakage across extraction boreholes and increasing gas concentration.Gas-bearing attributes are wide-spread among surrounding rock fractures found in coal seam gas extraction boreholes.In order to analyze the diffusion behavior of the grout and sealing mechanism across gas-bearing frac-tures,the multi-step methodology for scientific research was applied.First,an individual gas-bearing fracture grouting diffusion experiment was designed to clarify the propagation law of the grout front as well as the response law of grouting pressure.Then,by using the theoretical model for the diffusion of fracture grouting,the distributions of grout front and pressure for gas-bearing fractures were analyzed,disclosing the coupling effect between the liquid(grout)phase and the gas phase.Finally,based on distribution characteristic analysis for the pre-and post-grouting fractures in gas-bearing coal,the migration characteristic for the grout within coal fractures was studied by numerical simulation,as well as the sealing mechanism under the liquid-gas coupling effect.We found that the diffusion front of the grout for the gas-bearing fractures shows an apparent"U"distribution shape,which becomes gentle by the migration for the grout.The arc angle of the front decreases with increasing gas pressure,while it in-creases with larger fracture aperture,higher grout viscosity,and faster grouting rate.Among these factors,gas pressure exerts a more pronounced influence on grouting pressure compared to grout viscosity,fracture aperture,and grouting rate.A negative-pressure environment fa-cilitates faster grout diffusion in the central part of the fracture but slows down flow near the fracture walls,thereby increasing the arc angle of the diffusion front.A sharp pressure drop is observed at the liquid-gas interface within the fracture,and the liquid-gas coupling effect weak-ens as grout migrates and fracture aperture enlarges but becomes more significant with higher absolute gas pressure,greater grout viscosity,and increased grouting rate.Post-grouting anal-ysis reveals that large-aperture fractures in gas-bearing coal are significantly reduced or elimi-nated,with some of them partially filled by grout and transformed into small-aperture frac-tures,increasing the proportion of small fractures.Negative-pressure conditions promote grout penetration into small-aperture fractures,whereas positive gas pressure hinders grout entry into branched small fractures.These findings enrich the theoretical understanding of grouting sealing in gas-bearing fractures and provide practical guidance for efficient grouting and sealing of surrounding rock fractures of underground gas extraction boreholes.

Abstract:In order to study the influence of joint geometric characteristics on the effect of liquid CO2 blasting,based on the propagation characteristics of stress wave through liquid CO2 blas-ting,a incidence model of CO2 blasting stress wave was constructed under different joint geo-metric characteristics.Combined with LS-DYNA software and fractal dimension,the influence of joint length,width,inclination angle,curvature,and distance from the blast hole on the effect of liquid CO2 blasting was analyzed.The results show that joints have a significant bloc-king effect on the stress wave of liquid CO2 blasting,with a blocking coefficient generally be-tween 0.2 and 0.8.The degree of influence of the geometric characteristics of joints on the fluctuation of the blockage coefficient,from large to small,is as follows:joint spacing L,joint inclination angle θ,joint width d,joint curvature μ,joint length l.The rock damage caused by liquid CO2 blasting in jointed rock mass can be divided into two parts:fracture zone and blasting cracks.The fracture zone is mainly located between the blast hole and the joint,while the blasting cracks are mainly located around the blast hole and at the end of the joint.In addi-tion,by characterizing the damage of jointed rock mass through fractal dimension,it was found that the influence of joint geometric characteristics on the damage of liquid CO2 blasting rock masses,from large to small,is as follows:joint width d,joint length l,joint spacing L,joint inclination angle θ,joint curvature μ.A corresponding damage prediction model was es-tablished by combining regression analysis and linear fitting.The research results were experi-mentally verified in a gold mine in Song County,Luoyang,which effectively improved the blasting effect of jointed rock mass while reducing the construction amount,and promoted the promotion and application of liquid CO2 blasting technology.